apple: Add RLIMIT_RSS as alias of RLIMIT_AS

This is defined in <sys/resource.h> as

    #define	RLIMIT_RSS	RLIMIT_AS	/* source compatibility alias */

See http://opensource.apple.com//source/xnu/xnu-1456.1.26/bsd/sys/resource.h

Author: kamalmarhubi

src/unix/bsd/apple/mod.rs

@@ -726,6 +726,7 @@ pub const RLIMIT_DATA: ::c_int = 2;
 pub const RLIMIT_STACK: ::c_int = 3;
 pub const RLIMIT_CORE: ::c_int = 4;
 pub const RLIMIT_AS: ::c_int = 5;
+pub const RLIMIT_RSS: ::c_int = RLIMIT_AS;
 pub const RLIMIT_MEMLOCK: ::c_int = 6;
 pub const RLIMIT_NPROC: ::c_int = 7;
 pub const RLIMIT_NOFILE: ::c_int = 8;